For use in ultrasonic actuators, we investigated the structural and piezoelectric properties of (1 - x)Pb(Zr0.515Ti0.485)O3 - xPb(Sb1/2Nb1/2)O3 + 0.5 wt% MnO2 [(1 - x)PZT - xPSN + MnO2] ceramics with a variation of x (x = 0.02, 0.04, 0.06, 0.08). All the ceramics, which were sintered at 1250˚C for 2 h, showed a typical perovskite structure, implying that they were well synthesized. A homogeneous micro structure was also developed for the specimens, and their average grain size was slightly decreased to 1.3μm by increasing x to 0.8. Moreover, a second phase with a pyrochlore structure appeared when x was above 0.06, which resulted in the deterioration of their piezoelectric properties. However, the 0.96PZT-0.04PSN+MnO2 ceramics, which corresponds with a morphotropic phase boundary (MPB) composition in the (1 - x)PZT - xPSN + MnO2 system, exhibited good piezoelectric properties: a piezoelectric constant (d33) of 325 pC/N, an electromechanical coupling factor (kp) of 70.8%, and a mechanical quality factor (Qm) of 1779. The specimens with a relatively high curie temperature (Tc) of 305˚C also showed a significantly high dielectric constant (εr) value of 1109. Therefore, the 0.96PZT - 0.04PSN + MnO2 ceramics are suitable for use in ultrasonic vibrators.

Mg-doped and In-Mg co-doped p-type GaN epilayers were grown in a low-pressure metal organic chemical vapor deposition technique. The effect of In doping on the p-GaN layer was studied through photoluminescence (PL), persistent photoconductivity (PPC), and transmission electron microscopy (TEM) at room temperature. For the In-doped p-GaN layer, the PL intensity increases significantly and the peak position shifts to 3.2 eV from 2.95 eV of conventional p-GaN. Additionally, In doping greatly reduces the PPC, which was very strong in conventional p-GaN. A reduction in the dislocation density is also evidenced upon In doping in p-GaN according to TEM images. The improved optical properties of the In-doped p-GaN layer are attributed to the high crystalline quality and to the active participation of incorporated Mg atoms.

In submicron MOSFET devices, maintaining the ratio between the channel length (L) and thechannel depth (D) at 3:1 or larger is known to be critical in preventing deleterious short-channel effects. Inthis study, n-type SOI-MOSFETs with a channel length of 0.1µm and a Si film thickness (channel depth) of0.033µm (L:D=3:1) were virtually fabricated using a TSUPREM-4 process simulator. To form functioningtransistors on the very thin Si film, a protective layer of 0.08µm-thick surface oxide was deposited prior tothe source/drain ion implantation so as to dampen the speed of the incoming As ions. The p-type boron dopingconcentration of the Si film, in which the device channel is formed, was used as the key variable in the processsimulation. The finished devices were electrically tested with a Medici device simulator. The result showedthat, for a given channel doping concentration of 1.9~2.5×1018cm−3, the threshold voltage was 0.5~0.7V, andthe subthreshold swing was 70~80mV/dec. These value ranges are all fairly reasonable and should form a‘magic region’ in which SOI-MOSFETs run optimally.

The field of photocatalysis is one of the fastest growing areas both in research and commercial fields. Titanium dioxide is the most investigated semi-conductor material for the photocatalysis applications. Research to achieve TiO2 visible light activation has drawn enormous attentions because of its potential to use solar light. This paper reviews the attempts made to extend its visible photocatalytic activity by carbon doping. Various approaches adopted to incorporate carbon to TiO2 are summarized highlighting the major developments in this active research field. Theoretical features on carbon doping are also presented. Future scenario in the rapidly developing and exciting area is outlined for practical applications with solar light.

Lanthanum oxide was introduced to molybdenum powder by liquid-liquid doping and liquid-solid doping respectively. Mo alloys were prepared by powder metallurgy technology. The size distribution and feature of dopant particles and the fractographs of Mo alloys were investigated by TEM and SEM respectively. The results indicated that liquid-liquid doping method is favorable for refining and dispersing particles uniformly in matrix. Fracture toughness of Mo alloys prepared by liquid-liquid doping showed better results than that of liquid-solid doping. Furthermore, the influences of the size distribution of on properties of Mo alloys was discussed by dislocation pile-up theory.

Fe doped skutterudite CoSb3 with a nominal composition of FexCo1-xSb12 (0≤x≤2.5) have been synthesized by mechanical alloying (MA) of elemental powders, followed by vacuum hot pressing. Phase transformations during mechanical alloying and vacuum hot pressing were systematically investigated using XRD. Single phase skutterudite was successfully produced by vacuum hot pressing using as-milled powders without subsequent annealing. However, second phase of FeSb2 was found to exist in case of x≥2, suggesting the solubility limit of Fe with Co in this system. Thermoelectric properties as functions of temperature and Fe contents were evaluated for the hot pressed specimens. Fe doping up to x=1.5 with Co in FexCo4-xSb12 appeared to increase thermoelectric figure of merit (ZT) and the maximum ZT was found to be 0.78 at 525K in this study.

The initial irreversible capacity, Qi, is one of the parameters to express the material balancing of the cathode to anode. We introduced new terms, which are the initial intercalation Ah efficiency (IIE) and the initial irreversible specific capacity at the surface (Qis), to express precisely the irreversibility of an electrode/electrolyte system. Two terms depended on kinds of active-materials and compositions of the electrode, but did not change with charging state. MPCF had the highest value of IIE and the lowest value of Qis in 1M LiPE6/EC + DEC (1 : 1 volume ratio) electrolyte. IIE value of LiCoO2 electrode was 97-98%, although the preparation condition of the material and the electrolyte were different. Qis value of LiCoO2 was 0~1 mAh/g. MPCF-LiCoO2 cell system had the lowest of the latent capacity. Qis value increased slightly by adding conductive material. IIE and Qis value varied with the electrolyte. By introducing PC to EC+DEC mixed solvent, IIE values were retained, but Qis increased. In case of addition of MP, IIE value increased and Qis value also increased a little.

저압 유기금속 화학증착법을 사용하여 AIGaInP층의 diethylzinc의 III족 원소(AO, Ga, In)에 대한 비와 성장온도 변화에 따른 Zn(acceptor)의 첨가 농도특성을 연구하였다. Diethylzinc의 III족 원소(AI, Ga, In)비를 0.4에서 2.0까지 변화시켜 본 결과 0.85일 때 가장 높은 acceptor 농도를 가졌으며, 성장온도를 690˚C에서 800˚C까지 변화시킨 결과 성장온도에 대한 변화는 690˚C-730˚C일 때 온도가 증가함에 따라 acceptor농도는 커졌으며, 그 이상에서는 감소하였다. 또한, 성장속도가 빠를수록 높은 acceptor 농도를 가지게 되어 3.3μm/hr의 성장속도일 때 8x1017/㎤의 가장 높은 acceptor 농도를 얻을수 있다.

UO2-6wt%Gd2O3가연성 독물질 소결체에 미량첨가한 Al 화합물(Al(OH)3, ADS(aluminium disterate), Al(OH)3+ADS)이 소결성 및 미세조직에 미치는 영향을 고찰하고자 하였다. 이를 위하여 Al이 첨가된 UO2-6wt%Gd2O3압분체를 1700˚C, 수소 분위기에서 4시간동안 소결한 후 특성시험을 수행하였다 Al을 첨가한 UO2-6wt%Gd2O3의 소결밀도는 94% T.D.이상이였고, ADS를 이용한 Al 첨가가 개기공도 감소에 상대적으로 크게 기여하였다. 또한 Al을 첨가하면 10μm 이상의 큰 기공과 1μm 이하의 작은 기공은 많이 줄어들었고 첨가된 Al 화합물의 종류와는 무관하게 평균 기공크기는 2-3μm였다. 그리고 Al을 첨가하지 않은 소결체의 결정립은 이중 결정립 형태를 갖는 반면에 Al을 첨가하면 결정립은 균일하였다. 특히, ADS를 첨가한 소결체의 평균 결정립 크기는 4.6μm로 가장크게 증가하였다.